The present invention, in some embodiments thereof, relates to the fields of logistics and radio frequency communications and, more particularly, to RFID tags including an antenna that provide reasonable signal strengths when in the proximity of metal objects such as motor vehicles that is useful, for example, for fuel-purchase authorization.
To be successful, a service station generally dispenses fuel to as many vehicles as possible in a given period of time. This is achieved, for example, by providing high speed entrance and egress and many fuel-dispensing locations (i.e., fuel pumps), arranged for high-throughput refueling of many continuously arriving vehicles.
One preferred method for increasing the attractiveness of a service station is through the use of automated payment for fuel. In such methods, a vehicle is equipped with a vehicle identification tag storing data relating to the vehicle identity and a payment method. Each fuel-dispensing location is provided with a vehicle identification tag-reader including a tag reading transceiver provided with a vehicle identification tag reader antenna that is configured to wirelessly read the vehicle identification tag.
In order to reduce fuel theft and in order to reduce interference between identification tag readers, it is useful to limit the range of the wireless communication (as measured between the vehicle identification tag and the vehicle identification tag reader antenna), typically to only a few centimeters. Thus, vehicle identification tags are generally located in proximity of a vehicle refueling port and vehicle identification tag reader antennae are generally secured to a fuel-dispensing nozzle associated with a specific fuel-dispensing location so that the tag reader is able to read the identification tag substantially only when the fuel-dispensing nozzle engages the vehicle refueling port. Generally, associated with the vehicle identification tag reader is a tag reader station communication transmitter, configured to forward information read from a vehicle identification tag to a service station controller.
For example, in the PCT patent applications published as WO 2007/049273 and WO 2007/049274 of the Applicant are taught wireless vehicle identification tag readers as well as systems and methods using the wireless vehicle identification tag readers. As depicted in FIG. 1, a wireless tag reader 10 is configured to be secured to a fuel dispensing nozzle 12 and includes a wireless tag reading transceiver functionally associated with an identification tag reading antenna, a wireless station communication transceiver and an autonomous power source.
When it is desired to purchase fuel using such a wireless system, a fuel dispensing nozzle (such as 12 in FIG. 1) of a fuel dispensing location is placed inside the refueling port of a vehicle, bringing the tag reading antenna of the tag reader (such as contained within the casing of tag reader 10) in wireless communication range with a vehicle identification tag located in proximity of the refueling port. Information (such as vehicle identity, payment means) read by the tag reading transceiver of the tag reader through the tag reading antenna is forwarded to the service station controller by a wireless station communication transceiver (such as contained within the casing of tag reader 10) along with the identity of the fuel-dispensing nozzle with which the tag reader (e.g., tag reader 10) is associated. Based on the applicable rules, the service station controller optionally communicates an authorization signal including if, under what conditions and how much fuel to dispense to the identified vehicle to the service station controller which forwards the authorization signal to the appropriate fuel dispensing location through the existing wired communication.
In order to reduce costs, a wireless tag reader such as 10 is designed to be easy install and remove, allowing simple and cheap hardware upgrading. Due to the simplicity of such wireless tag readers and the ease with which the wireless tag readers may be attached and reattached to a fuel dispensing nozzle, it is often simpler and cheaper (and thus preferred) to discard a wireless tag reader with a spent power source rather than to recharge or replace the power source. It is thus preferred that wireless tag readers, such as 10 be as energy efficient as possible. Energy efficiency allows a given power source to be used for as long as possible before replacement of the entire tag reader.
It is also desirable that the vehicle identification tag to be read by a wireless tag reader be cheap, easy to install and maintenance free. One possibility is to use a vehicle identification tag that is substantially an RFID (radio-frequency identification) tag whether a powered RFID tag or a passive RFID tag.
Preferably, a passive RFID tag which is substantially a passive radio-frequency RFID generally made up of a loop (magnetic dipole antenna) antenna and an electrical circuit is used. The vehicle identification tag is placed in proximity of the fuel inlet port of a vehicle. When the fuel dispensing nozzle (such as 12) is placed in the fuel inlet port, the antenna of the tag reader (such as 10) is close to the antenna of the vehicle identification tag. The tag reader is activated to produce a time-varying magnetic field that passes through the loop of the antenna, inducing an electromotive force which functions as a source of electrical power for the electrical circuit of the tag. The electrical circuit of the tag uses the received power to transmit the required data. Exemplary such devices are described in the PCT patent application published as WO 2007/049274.
It is known that it is challenging to use passive RFID tags of the frequencies suitable for short range transmission (generally, less than about 100 MHz, e.g. 13.56 MHz or 125 KHz) in the proximity of conductive materials such as a metal object (such as a vehicle body) due to the generation of eddy currents in the conductive material which generates a magnetic field opposite to the reader magnetic field, significantly attenuating the magnetic flux through the RFID tag antenna coil, reducing the amount of current induced in the RFID tag antenna coil. It is possible to place the antenna of an RFID tag at a distance from the metal object in order to minimize the negative effects, but such distancing is not practical for use with vehicle identification tags. It is preferred that the vehicle identification tag be unobtrusive and thin so as not to interfere with normal use of the fuel nozzle and to avoid physical damage to the identification tag.
It is known to interpose a sheet of electromagnetic shielding material between an RFID antenna and a conductive material such as a metal so as to reduce the eddy currents and consequently the magnetic field induced in the conductive material (see for example, data sheets for TDK Flexield® (TDK Corporation, Chuo-ku, Tokyo, Japan). The greater the permeability (μ) of the shielding material the greater the reduction of the eddy currents in the conductive material and consequently the stronger the magnetic field produced by the reader that passes through the antenna from the tag. However, it has been found that using an electromagnetic shielding material does not reduce eddy currents sufficiently to allow a desired degree of energy savings when reading an RFID secured in proximity of a refueling port of a motor vehicle.
It would be highly advantageous to have a thin RFID tag that is less susceptible to the effects of a conductive material such as a metal object. For example, it would be highly advantageous to have a passive radio-frequency RFID tag that, when associated with the metal body of a vehicle, provides a reasonable signal with relatively low energy use.